Process and compound for coloring the surfaces of metal articles



Patented Nov. 29, 1938 PATENT OFFICE PROCESS AND COMPOUND FOR COLORING THE SURFACES O-F METAL ARTICLES Leslie Culling-wood Fenwicke, London, England No Drawing. Application September 25, 1937, Serial No. 165,778. In Great Britain September 29, 1936 6 Claims.

This invention is for improvements in or relating to processes and compounds for coloring, e. g. blueing the surfaces of ferrous metal articles. Processes are known in which the articles to be colored are immersed in a bath of mixed chemicals comprising caustic alkali, an alkali cyanide and litharge with or without other salts. It has-hitherto been usual when preparing the coloring bath to weigh out the chemicals separately and to introduce them separately and successively into a bath of water whereafter the liquid mixture is thoroughly agitated. This method for the preparation of the bath has led to considerable wastage due to splashing and since the caustic alkali is usually employed in quantities to produce a solution of high concentration such splashing may be attended by injury to the person preparing the bath.

According to this invention, a method of preparing a bath for coloring, e. g. blueing, ferrous metal articles consists in forming a powdered mixture comprising caustic alkali, an alkali cyanide and an oxidizing agent with or without other metal salts, and introducing the mixed powders into a water bath which is heated preferably after the introduction of the powdered mixture.

It will be appreciated that by supplying the materials already mixed in the correct proportions, considerable time is saved in preparing or replenishing the bath as compared with the usual method in which each chemical is separately weighed and introduced into the bath. Furthermore, by introducing the mixture in powdered form splashing is not so liable to take place and if it does take place it does not ,lead

to the loss of any one particular constituent of the mixture and thus the proportions of the chemicals in the bath remain unaffected.

A process for coloring, e. g. blueing, ferrous metal articles according to this invention consists in steeping the articles in a bath prepared in the manner outlined above and in which. the powdered mixture comprises caustic soda, sodium cyanide, lead oxide, lead acetate. In the above mixture the lead oxide is employed as the oxi-' dizing agent. a

. When a mixture of the kind last referred to above is employed blueing of the surfacesvis effected in as small a time as one-and-a-half minutes and at a temperature between 100 and 135 C The preferred composition of the powder is:-

Parts per weight These ingredients are mixed together in dry powdered form and are preferably stored and dispensed in a moisture-proof container; Caustic soda is hygroscopic and thus the moistureproof container maintains the powder in a dry condition and in a condition which enables the powder readily to be introduced into the bath of water. The above composition is preferably used with 50 parts by weight of water. The mixture is introduced into cold water contained in an iron bath and the temperature of the bath is raised up to about 130 C. when it is ready for use. The articles to be colored are steeped in the hot aqueous mixture for a period from 2-4 minutes according to the depth of coloring required. After the expiry of about 4 minutes a deep blue color is obtained and if a nearly black color is required, they are allowed to steep for a further period.

In applying the process referred to above to treating articles engraved or stamped with markings, the markings may be filled subsequently to the blueing process with a hard drying paint or enamel of a contrasting color, for example white. Preferably the paint or enamel is applied in the form of a paste which is smeared over the marked surface and allowed to dry or nearly dry whereafter the excess may be removed by a. suitable solvent, thus leaving the filled markings clear cut. This method is particularly applicable to articles marked with graduations and scales such as rifle sights, micrometers and other measuring instruments by which quick and accurate readings may be obtained.

I claim:-

1. A process for coloring the surfaces of ferrous metal articles, which consists in steeping the articles in a bath comprisingan aqueous solution of caustic soda, sodium cyanide, lead oxide and lead acetate.

2. A process for coloring the surfaces of ferrous metal articles, which consists in steeping the articles in a bath which has been prepared by the introduction into water of a powdered mixture, comprising caustic soda, sodium cyanide, lead oxide, lead acetate, which bath is heated after the introduction of the powdered mixture.

3. A process for coloring the surfaces of ferrous metal articles, which consists in steeping the articles in a bath prepared by the introduction into water of a powdered mixture, comprising caustic soda, sodium cyanide, lead oxide, lead acetate, which bath is heated to a temperature between- 100 and 135 C. after the introduction of the powdered mixture and in leaving the articles immersed in the hot bath for a period of one-and-a-half minutes upwards.

4. A composition for the preparation of a bath for coloring the surfaces of ferrous metal articles, comprising a powdered mixture of caustic soda, sodium cyanide, lead oxide and lead acetate.

5. A composition for the preparation of a bath for coloring the surfaces of ferrous metal articles, comprising a powdered mixture consisting of 36 parts by weight of caustic soda, '7 parts by weight of lead oxide (litharge), 2 parts by weight of sodium cyanide, 2 parts by weight of lead acetate and 1 part .by weight of monowater, which aqueous mixture is raised to a temperature from between 100 to 135? C.

LESLIE COLLJNGWOOD FENWICKE. 

